There is an increasing number of hemodialysis patients in whom creation and maintenance of an arteriovenous fistula is difficult or even impossible. For these patients, one prior art long-term catheter has provided a reasonable solution to their problems. It provides good blood flow and can be left in place in the external or internal jugular vein for many months or even years. The flow characteristics of this catheter are not ideal, but a plain tube catheter with an open end appears to maintain patency better than that of a tapered tube with side ports. The main problem with this plain tube catheter is its cross-sectional shape, which is similar to a double-barreled shotgun, and its' squared off ends. These features make it unsuitable for percutaneous insertion over a wire guide. As a result, this plain tube catheter has to be introduced with a cut-down surgical technique, which requires considerable time and skill.
A more serious problem with the plain tube catheter is that once it has been removed, it can not easily be reinserted into the same site. Therefore, jugular vein sites are soon used up and no longer available to the patient. One physician has used a peel-away sheath for percutaneous insertion of this catheter, but a very large 18 French sheath was required to accommodate the largest cross-sectional dimension of the catheter. Most physicians would judge the size of an 18 French introducer sheath to be undesirable.
Heretofore, it has always been considered necessary for the positive pressure return lumen to extend beyond the negative pressure intake lumen of a hemodialysis catheter. This is to ensure that blood returning from a hemodialysis treatment machine is delivered downstream from blood being extracted for purification. However, a problem with this configuration is that clots tend to adhere to the outside wall of the catheter at the entrance port to the shorter, negative pressure intake lumen.
To provide modern high efficiency dialysis, it is also desirable to utilize a catheter having two large diameter lumens for high blood flow rates and also having an external cross-sectional dimension which is not too large for vascular access. One such temporary access or short-term catheter includes a simple double-D lumen configuration. The walls of the catheter are thin, and the equal area lumens make full use of the available space. However, to insure that this catheter keeps its shape during high flow rate dialysis, the catheter is made of relatively stiff material which is unsuitable for long-term placement. If this temporary catheter is made of a silastic material, the intake lumen collapses under the influence of the strong negative intake pressure. Furthermore, the septum between the two lumens is pulled into the negative pressure lumen, thereby adversely changing the cross-sectional area in the two lumens as well as the blood flow rates therethrough.
Temporary or short-term catheters of the double-D configuration are used in large numbers all over the world, but they have a disconcerting tendency to get blocked. These catheters are made of a relatively stiff material to prevent the lumens from collapsing. A problem with the stiff material is that the catheter kinks or buckles when bent more than 180.degree.. This also leads to lumen obstruction and the potential risk of cracking or splitting the wall. Furthermore, catheter stiffness combined with a tapered end for insertion over a guide wire has been responsible for many penetrating injuries of the wall of the superior vena cava or right atrium. There have been many deaths caused by such spontaneous perforations. This can occur by erosion, days or weeks after the catheter is originally inserted. However, no penetrating vein wall injuries have been reported with the use of blunt-end silastic catheters.
Silastic catheters with the double-barreled shot-gun configuration (two cylindrical lumens side by side) are remarkably resistant to kinking even when bent sharply through 180.degree.. Also a cylindrical lumen is the theoretical optimum to achieve maximum flow for the smallest surface area of the wall. Finally, the cylindrical lumen avoids the sharp corners in the wall of the double-D configuration where, at least theoretically, clotting is more likely to occur.
The side-by-side open-ended design of the long-term catheter has much less tendency to block, but has not been used as a temporary catheter since it cannot easily be introduced percutaneously. The circular intake lumen of the long-term catheter is similarly recessed back from the distal end of the return lumen to minimize blood recirculation. A problem with this is that the wall of the extended positive pressure return lumen provides a surface for clots to adhere. In an attempt to solve this blockage problem, the walls of the negative pressure intake lumen are provided with side ports. However, it is believed that these side ports may actually encourage clotting.
The long term catheter typically employs a fixed-position dacron cuff which may not be conveniently positioned to stabilize the catheter. Removal of the catheter and release of the dacron cuff requires a new incision and dissection of the cuff by a surgeon. Dissecting the cuff from ingrown tissue invariably leads to bleeding, which may be hard to control.